1. Technical Field
This disclosure relates to measurements systems and methods and more particularly, to a system and method for measuring sub-quarter micron dimensions in semiconductor devices. These dimensions are known as critical dimensions (cd).
2. Description of the Related Art
In semiconductor fabrication critical dimensions below 1 micron are typically measured with topdown scanning electron microscopy. Although a useful measurement tool, scanning electron microscopes have several disadvantages. These disadvantages include, among other things, charging a sample to be measured and increased risk of contamination.
Scanning electron microscopy (SEM) is used principally to provide images at or near the surface of a solid, such as a semiconductor chip. By scanning an electron beam across the surface of a specimen, a one-to-one correspondence can be set up in the positions of the probe upon the specimen and the electron beam on an imaging device, for example an oscillograph. The signal produced is brightness modulated to provide a visual image. As described, SEM requires the bombardment of the specimen with an electron beam. This charges the specimen and may cause damage to semiconductor devices. Further, the electron beam may produce mass transport of atoms on the specimen which may lead to contamination of various regions of the semiconductor device.
SEM and atomic force microscopy (AFM) are also limited, in that, these techniques primarily measure individual structures on the surface of a semiconductor device rather than structure assemblies.
Therefore, a need exists for a method and system with improved resolution for sub-quarter micron measurements. A further need exists for a method and system for making such measurements without charging on contaminating a sample being measured. A still further need exists for performing such measurements on structure assemblies thus improving the statistical value of the measurement. For this, we suggest to equip a conventional micro-ellipsometer with a revolving stage realizing a new kind of measurement tool which we call an Anisotropy Micro-Ellipsometer (AME) (i.e., a revolving ellipsometer). As will be explained, such an AME allows the measure of critical dimensions (cd) of sub-micron structure assemblies with high resolution without any of the aforementioned drawbacks. Conventional ellipsometry is well known in the art, and offers the advantage of being non-destructive and non-invasive to a sample. Conventional ellipsometers are used to measure optical parameters of surfaces and thicknesses of films which cover surfaces. For this, measurements on stationary samples are performed.